This invention relates to a process for disposing of chlorinated organic compounds, and more particularly to the conversion or decomposition of such compounds generated while producing a metallic chloride by chlorinating a metallic oxide in the presence of a carbon reductant.
Metallic chlorides are used for a variety of purposes including production of metal from metallic chloride salts, such as the production of aluminum from aluminum chloride, for example.
By a well-known process, metallic chlorides are commercially synthesized by chlorinating a metallic oxide in the presence of a carbonaceous reducing agent. Production of metallic chlorides by such a process, however, generates chlorinated organic pollutants, such as hexachlorobenzene. In many uses of metallic chlorides the chlorinated organic by-products must be separated from the chlorides. After separation, the chlorinated organic materials present a difficult disposal problem because they are not readily incinerated and landfill disposal is expensive. Processes for decomposing or converting chlorinated organic materials into compounds which may be safely disposed of or futher used are, therefore, desirable.
Processes are known for the destruction of chlorinated organics. For example, Japanese Pat. No. 7,246,673 describes a process whereby AlCl.sub.3 vapors containing hexachlorobenzene as an impurity are brought into contact with a suitable metal in a solid or molten state maintained at a high temperature. Upon contact with the hot metal, the hexachlorobenzene decomposes into carbon and chlorine. The carbon is deposited in or on the metal and the chlorine is given off as a gas. Over time, the buildup or concentration of carbon slows the activity of the metal, and it is reactivated by exposing the heated metal to air which removes the carbon by oxidation.
Another process for removing hexachlorobenzene is described in Japanese Pat. No. 7,240,960. In this process, AlCl.sub.3 gas containing hexachlorobenzene is brought into contact with a bed of alumina heated to a temperature of 500.degree. C. to 1200.degree. C. According to the patentees, the alumina reacts with hexachlorobenzene to produce AlCl.sub.3, carbon and carbon monoxide, and thus breaks down the objectionable chlorinated hydrocarbon.
In a process for making AlCl.sub.3 described in Russell et al U.S. Pat. No. 3,842,163, an alumina having a low alpha phase content is chlorinated in the presence of carbon to produce AlCl.sub.3. Low alpha phase content alumina is the desired feedstock because alpha phase alumina has a lesser surface area per particle than other phases such as gamma, for example, and it is therefore less reactive. Because the more reactive alumina material used in the process described by Russell et al preferentially reacts with the available chlorine, the alpha alumina remains unreacted and accumulates in the reactor with continued use. Accumulated alpha alumina, referred to as spent bed material, must be removed from the reactor from time to time to avoid adversely affecting efficient operation of the reactor, and disposal thereof has been a problem.